Automatic dynamic compander system

Abstract

In a circuit for the automatic dynamic compression or expansion of a signal between its input and its output, the circuit presenting a useful signal path connected between its input and its output and containing a setting member which is electronically controllable for varying the transmission factor between the circuit input and output, the circuit also presenting a branch path connected at one point to the useful signal path and containing a control voltage generator for generating, from the signal in the useful signal path, a control voltage applied to control the setting member, there is also provided a second setting member connected in the branch path and arranged to be electronically controllable for varying the transmission factor exhibited by the branch path, and means connecting the output of the control voltage generator to the second setting member for effecting a counterregulation of the transmission factor of the branch path, relative to the transmission factor variation imparted to the useful signal path.

I claim: 
     
       1. In a circuit for the automatic dynamic compression or expansion of a signal between its input and its output, the circuit presenting a useful signal path connected between its input and its output and containing a first variable gain member which is electronically controllable for varying the transmission factor between the circuit input and output, the circuit also presenting a branch path connected at one point to the useful signal path and containing a control voltage generator for generating, from the signal at such point in the useful signal path, a control voltage and means applying the control voltage to the variable gain member, for causing the transmission factor of the useful signal path to have a value dependent on the value of the control voltage, the improvement comprising: a second variable gain member connected in said branch path and arranged to be electronically controllable for varying the transmission factor exhibited by said branch path; and means connecting the output of said control voltage generator to said second variable gain member for effecting a counterregulation of the transmission factor of said branch path, relative to the transmission factor variation imparted to said useful signal path. 
     
     
       2. A circuit as defined in claim 1, wherein the transmission factor variation produced by said second variable gain member in response to control voltage variation is substantially the same as that of said first variable gain member. 
     
     
       3. A circuit as defined in claim 1, wherein the transmission factor variation produced by said second variable gain member in response to control voltage variation is complementary to that of said first variable gain member. 
     
     
       4. A circuit as defined in claim 1, wherein said first and second variable gain member constitute means for causing the dependence of the useful signal path transmission factor on the control voltage to differ by only a constant factor from the dependence of the branch path transmission factor on the control voltage. 
     
     
       5. A circuit as defined in claim 1, further comprising filter means connected for dividing the frequency band of the signal in at least one of said branches into partial frequency ranges, and means in said one of said branches for varying the transmission factors associated with different ones of said frequency ranges independently of one another. 
     
     
       6. A circuit as defined in claim 1, for effecting automatic dynamic compression, wherein the signal applied to said circuit input varies in amplitude over a range which includes a low amplitude portion and a high amplitude portion, and comprising means for causing the low amplitude portions of such signal to be increased relative to the high amplitude portions between said circuit input and output, and comprising means for limiting the extreme of the transmission factor variation relating for the low amplitudes to a selected value causing a maximal increasing of the low amplitudes. 
     
     
       7. A circuit as defined in claim 1, wherein said control voltage generator comprises means for producing a direct voltage constituting the control voltage and means responsive to the signal at the input to said generator for causing: the direct control voltage to be produced when the generator input signal exceeds a threshold value; the direct control voltage to vary rapidly in one amplitude direction for varying the branch path transmission factor in a direction to cause the input signal to said generator to decrease below the threshold value; and the direct control voltage to vary slowly in the opposite amplitude direction until the input signal to said generator again exceeds the threshold value. 
     
     
       8. A circuit as defined in claim 7, constituting a dynamic compression circuit in which the output signal in said useful signal path varies in the same manner as the input signal to said control voltage generator. 
     
     
       9. A circuit as defined in claim 7 wherein, in said control voltage generator, said means for producing a direct voltage comprises a capacitor and said means responsive to the signal at the generator input comprise an electronic switch connected to said capacitor and arranged to become conductive when the generator input signal exceeds the threshold value for rapidly varying the voltage across said capacitor in such one amplitude direction thus producing the control voltage across said capacitor, and voltage supply means and resistance means connected for periodically charging said capacitor under control of the operation of said switch.